The effect of wind on hanging overhead signs can produce conditions that are at best annoying and at their worst can cause severe injury to property and people and occasionally even death. An erraticly swinging sign can severely damage traffic signals, supporting poles, electric lines, and span cables. If conditions are severe enough, a wildly swinging sign can cut through electric cables causing them to fall to the ground below, can shear off supporting poles, and can itself break lose to become a flying guillotine. In any of these cases, the resulting pole tops, electrical cables, and the sign itself all can become lethal instruments of death and destruction.
In general, four approaches have been taken to solve this problem. In the first, the sign is permitted and even encouraged to swing freely in order to "spill" the wind (U.S. Pat. No. 4,520,984, Rouleau, R. J., June 4, 1985 and U.S. Pat. No. 4,089,129, Patterson, W. W., May 16, 1978). Although such free swinging brackets allow the sign to swing within limits and thus avoid many of the more serious problems, the freely swinging sign is likely to wear and eventually fail at the pivot points and is still an annoyance and distraction to the motorist who must attempt to read and follow its directives.
A second approach is to attach a second "tether" cable to the bottom of the sign. The use of such a second tether cable is illustrated in U.S. Pat. Nos. 3,916,265 and 3,989,217, Friedman, Jack J., Oct. 28, 1975 and Nov. 2, 1976, respectively, where it is used to stabilize a traffic signal rather than a sign. When a taut tether cable is attached to the bottom of a sign, there is a pronounced tendency for both the upper and lower cables to resonate with an up and down motion producing severe "loading" on the supporting poles to which the cables are attached. Such loading can loosen the pole from the ground or, more seriously, can cause high tension lines often attached to the pole to come in contact with each other or with other objects.
A third approach has been to attach weights to the bottom of the sign. When the support attachment at the top of the sign is rigid, severe winds cause flexing of the sign and eventual metal fatigue of the sign plate itself. Such flexing has been eliminated to some extent by the attachment of a modified light-weight flanged channel material along the vertical edges of the sign. If a free swinging device is used to attach the sign to an overhead support, the added bottom weight causes additional wear at the pivot points.
A fourth approach has been to drill large holes in the sign itself in order to allow the wind to pass through the sign. Although this greatly reduces the swinging motion of the sign, the "swiss cheese" appearance of these signs leaves much to be desired aesthetically.